This invention relates to new compounds of diphenyl ether series possessing a very strong herbicidal activity, a process for preparing same and a herbicide comprising the new compounds as active ingredient.
Many compounds of diphenyl ether series have been examined hitherto to determine their effects in practical use as herbicides. In many cases, the presence or absence, degree, mode of function, selectivity and duration of the herbicidal activities of these compounds are markedly variable according to even a slight difference in chemical structure of these compounds such as sort, number and position of substituents thereof. Thus, it is extremely difficult to estimate the herbicidal activity of these compounds from their similarity in chemical structure.
It is a well-known fact that some compounds of diphenyl ether series are excellent herbicides. For example, 2,4-dichloro-4'-nitrodiphenyl ether (referred to hereinafter as NIP) and 2,4,6-trichloro-4'-nitrodiphenyl ether (referred to hereinafter as CNP) are widely used as herbicides in rice fields.
Ideal herbicides are required to exhibit on one hand a very strong herbicidal activity to undesirable plants even at a low level concentration and on the other hand an extremely low toxicity to useful plants. However, herbicides developed hitherto still fail to meet fully either or both of these requirements. In recent years, a problem of environmental pollution has also arisen in the field of agricultural agents and the use of a highly effective compound in a small amount is recommended to minimize any harmful side effect of the compound. Under these circumstances, there is a great demand for developing a new type herbicide which fully meets the aforesaid requirements.